Heat exchangers



July 20, 1965 A. M. GOODLOE HEAT EXCHANGERS Filed April 12, 1961 I INVEN TOR.

mm (mm AT TOR NE Y5 United States Patent 3,195,627 HEAT EXCHANGERS Alfred Minor Goodies, Westrieid, Ni, assignor to General Cable Corporation, a corporation of New Jersey Filed Apr. 12, 1961, Ser. No. 162,497 '13 Ciaims. (Cl. 165-131) This invention relates to heat exchangers. It relates more particularly to heat exchangers having tubes and in which heat is to be transmitted between a fluid flowing in the tubes and another fluid flowing over the outside surfaces of the tubes.

When fluid flows through heat exchanger tubes without restriction in same, there is a tendency for the heat transfer to be confined largely to the layers of fluid in Contact with the inside surface of the tube. In order to increase the rate of heat transfer, tubes have been equipped with certain types of internal fins so as to increase or extend the area of surface contact with the fluid, but such inside fins do not always cause a sufficient turbulence to prevent stratifying of the fluid flowing through the tube with the resulting heat transfer confined largely to the outer layers of the fluid stream.

It is an object of this invention to provide an improved heat exchanger with inserts in the tubes, and with the insert in each tube made of a knitted wire mesh material bonded to the inside surface of the tube. The wire mesh produces a large area of contact with the fluid in the tube and this area is diversified through the tube so as to increase the intimacy of contact of the metal with the fluid.

One of the advantages of the invention is that the heat exchangers are more economical to manufacture and another is that the insert does not interfere with bending of the tubes where a heat exchanger is designed for coiled tubing or for other tubes which require some curvature along the length of the tube.

Another object is to provide an improved method of making heat exchangers. According to this method, metal wire is knitted into a mesh material which is then brought together transversely to produce a mass of knitted mesh having a substantial cross section for filling or partially filling the interior of the tube. The wire mesh insert is pulled into the tube and bonded to the inside surface of the tube by several different methods.

Another object of the invention is to provide a knitted metal wire insert in a heat exchanger with a special knit that prevents necking down of the insert when subjected to substantial pull in long tubes.

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views;

' FIGURE 1 is a fragmentary, large-scale view of the knitted wire mesh material of which the insert is made;

FIGURE 2 is a diagrammatic view showing the tubular cross section of the knitted wire mesh material before it is brought together transversely of its length to form the insert;

FIGURE 3 is a diagrammatic, sectional view, taken on the line 33 of FIGURE 5, showing apparatus for making the inserts from the material shown in FIGURE 2, but with one wheel omitted for clearer illustration;

FIGURE 4 is a sectional view taken on the line 44 of FIGURE 3;

FIGURE 5 is an end view of the apparatus shown in FIGURE 3, the view being taken on the plane 5--S of FIGURE 3;

3.,ih5527 Patented July 20, 1965 ice FIGURE 6 is an enlarged, fragmentary view showing a portion of a heat exchanger made in accordance with this invention;

FIGURE 7 is a sectional view taken on the line 7-7 of FIGURE 6; and

FIGURES 8, 9 and 10 are sectional views, similar to FIGURE 7, but showing modified constructions of the insert.

A wire is knitted to form a mesh material 16 having small needle loops 18 and substantially larger segment loops 2!). The advantage of this particular knit is that pull applied in the direction of its length, as indicated by the arrow 1, does not result in any substantial narrowing down of the width of the knitted mesh. Thus, an insert made of a mass of the knitted mesh 16 can be pulled longitudinally without having the mass necked down to a smaller cross section as would occur with conventional knitting having the needle loops and segment loops of substantially the same size.

The wire 15 may be copper wire so as to give the heat exchanger a high rate of heat conduction. For uses where copper wire would be injured by the fluid flowing through the heat exchanger, other kinds of metal wire can be used, such as stainless steel.

The wire 15 may be of various diameters. The only limitation on the size of the wire is that it be of a diameter that can be knitted. The advantage of using wires of as large a diameter as possible is that the larger wire has a cross section capable of transmitting greater quantities of heat. In practice, the invention is made with wires of from 0.020 to 0.025 inch, with good results; but larger wires can be knitted with special apparatus.

The stiffness of the wire is not very important because in choosing wires of large diameters for knitting, sufficient stiffness for the insert is obtained. It will be evident that more stiffness is required for inserts in larger tubes, but this stiffness can be obtained by the particular shape of the insert, as will be more fully explained, and is not entirely dependent upon the stiffness of the wire.

FIGURE 2 shows the knitted mesh material in the form of a tube 24, and it is preferable that the material be knitted in the form of a tube having a diameter suitable for the apparatus by which the material of the tube is brought together transversely to form an insert for a heat exchanger tube. The tube 24 is shown partially flattened, but when it is to be passed through an insertforming apparatus 26 (FIGURE 3), the tube 24 is opened up and passed over a bulb 28.

A stem extends from the bulb 28 and is preferably of integral construction with the bulb. Then the stem 33 is shaped to give the insert the particular cross section desired. In the apparatus shown in FIGURES 3-5, the stem 30 has four fins 32, and the knitted mesh material 16 is forced into the space between the fins 32 by compression wheels 36 located at angularly-spaced locations around the stem 39, as shown in FIGURE 5.

The bulb 28 and stem 34 are held against axial move ment by a support 40 (FIGURE 3) extending through the tube 24 from a location beyond the end of the tube. The inserts are made as separate lengths equal to the length of the heat exchanger tube in which they are to be used. Wheel brackets 41 are held by set screws 42.

When the mesh material 16 comes from the apparatus 26, it has the general shape of a cross, this finished insert being indicated by the reference character 16 in FIG- URES 6 and 7. The insert 16 is pulled into a tube 44. The inside diameter of the tube 44 is slightly less than the diameter of a circle circumscribed through the ends of the branches of the insert 16' as the insert originally comes a from the apparatus which forms it. These branches of the insert 16 will be referred to as spokes 46 and it will be evident that the insert can be made with more or fewer, spokes 46, but preferably not fewer than three.

Because of the fact that the inside diameter of the tube 44 is sli htly less than a circle circumscribed through the ends of the spokes 46, it will be evident that the spokes will be compressed radially to some extent when the insert is pulled into the tube 44, and thus the insert exerts some pressure against the inside surface of the tube 44.

The insert 16' should be bondedtothe inside'surface ofthe tube in order to increase the rate of heat flow, and also to prevent possible corrosion of the surface of the wire that touches the inside surface of the tube. This bonding of the wire loops to the tube surface can be done in several ways.

One way is to coat the wire of the insert 16 with solder and also to coat the inside surface of the tube 44 with solder. After the insert has been pulled into the tube,

the assembly is heated high enough to fuse the solder, and when the assembly cools, the loops adjacent to the surface of the tube are bonded by the merging of their solder .coats while' molten.

Another way of bonding the insert to the tube is by flowing molten solder through the tube after the insert isin' place. This molten solder passes along the inside surface of the tube and contacts with those loops of wire which are close to the surface and effects a soldering of the wires to the wall of the tube.

One other method that can be used is to heat the tube with the insert in place, the heating being carried out electrically or otherwise to the proper temperature and the tube and insert assembly then beingput in a level position and partially filled with hot solder. While in this condition the tube is revolved and as the end of each spoke of the insert passes below the level of the molten solder, the wires adjacent to the wall of the tube pick up sufi'icient solder to bond them to the tube Wall when the solder partially filling the tube is removed and the assembly is allowed to cool.

FIGURE 8 shows the tube 44 with an insert 16a having spokes 52 in a somewhat different relation to one another than in the cross section illustrated in FIGURE 7. Where larger tubes are used or the knitted wire has less stifiness, an insert 16]; may be used. This insert has five spokes 54 and is of generally starlike cross section. It will be evident that the inserts can be made withany number of spokes provided that the original tube is of sufiicient circumference to provide the length necessary for a perimeter having the increased number of spokes.

The insert cross sections shown in FIGURES 6-9 only partially fill the tube 44 and there are empty spaces within the tube through which liquid flows, though with some turbulence caused by the proximity of the knitted mesh surfaces of the insert.

Where a maximum heat transfer is important and the, rate of flow is not sufiicient to cause excessive'pressure drop through the tube 44, the construction shown in FIGURE 10 can be used. In this construction, the metal mesh material is confined transversely into an insert 160 which completely fills the inside cross section of the tube 44 with the loosely knit mesh material 16. This insert 16c can be made by gathering the knitted mesh material transversely, or folding it over on itself, or in any other way that confines the knitted wire mesh loops into a substantially uniform mass of mesh material across the full inside diameter of the tube 44.

The undistorted cross section of the insert 16c must be slightly greater than the inside of the tube 24 so that the insert 160 is under some compression when assembled with the tube 44. This is important because soldering can only be accomplished when there is pressure exerted between the loops of wire of the insert and the inside wall of the tube at the lOcaL Qns where the loops of wire touch the tube.

With all of the constructions illustrated in FIGURES 6-10, the knitted wire mesh of the insert is capable of stretching and compressing as necessary to permit the tube 44 to be wound into a coil, or to be given any curvature necessary for the particular heat exchanger in which the tube is to be used.

It will be apparent that the heat exchanger of this invention can be used equally well for transmitting heat to a fiuid flowing through the tube 44 or for removing heat from such a fluid. Whether heat flows into or out of the fluid in the tube depends upon the temperature of the fluid that flows over the outside of the tube during the heat-exchange operation. I

The inserts made of knitted wire mesh material, in accordance with this invention, provide a foraminous structure which extends from the central portion of the tube to the inside surface of the tube walls and which contacts with the tube walls at the many points where loops of the mesh touch the walls. The cross sectionfor heat transfer to the walls is increased by the bonding solder or other metal which connects the loops of wire with the inside surface of the tube.

' ducting bonding means. When the wire used is stainless steel and the tube is stainless steel, the wire will ordinarily be welded to the inside surface of the tube.

In order to prevent the knitted wire mesh from adding substantial resistance to the flow of liquid or gas through the tube 44, the insert is preferably madetof a mesh having an open type of knit. This means that the spaces between the wires of the different loops are substantially wider than the diameters of the wires. Such an open type of knit is illustrated in FIGURE 1; but the degree of opening need not be so great as FIGURE 1 where the rate of fluid flow is small and a high rate of heat transfer is desired.

The preferred embodiment of therinvention has been 7 illustrated and described, but changes and modifications can be made and some features can be used in different combinations without departing from the invention as defined in the claims.

What is claimed is:

I 1. A heat exchanger including a metal tube,

(a) a knitted wire mesh insert formed of wire loops and located within the tube,

(b) the insert being of much greater length than width and having its length extending axially in the tube,

(c) the loops being crowded together transversely of the length of said insert out with the crowded loops of the wire mesh in position to contact with fluid flowing along the inside of the tube to produce turbulence of the fluid adjacent to the wire mesh,

(d) the insert being shaped with partition or wall portions of double wall mesh and having a symmetrical pattern about a longitudinal axis of the tube, the partition portions dividing the interior of the tube into a plurality of axially-extending passages,

(e) the partition portions having faces spaced from the inside surface of the tube across extending angular'spans of the circumference of the'tube so that said faces and the sides of the tube form sides of said passages,

(f) the partition portions at the outer radial limits of the double wall mesh touching the inside surface of the tube in heat-exchanging relation therewith, and

(g) heat-conducting bonding material securing wire loops at said outer radial limits of the partition portions to the inside surface of the metal tube whereby the partition portions remain in contact with the inner peripheral surfaces of the tube in spite of bend= ing of the length of the tube to arcuate shapes.

2. The heat exchanger described in claim 1 characterized by the partition portions being resiliently compressible in directions parallel to said faces whereby the insert fits into a tube of a diameter somewhat smaller than the original width of the insert prior to its insertion into the tube.

3. The heat exchanger described in claim 1 and in which the insert is made of a single length of wire.

4. The heat exchanger described in claim 1 and in which the insert is made of a knitted wire mesh having needle loops and segment loops with the needle loops substantially smaller than the segment loops, and the rows of knit-ting extend transversely of the length of the tube whereby the insert can originally be pulled into the tube without necking down of the insert to a substantially smaller diameter as a result of the longitudinal pull on the insert.

5. The heat exchanger described in claim 1 and in which the tube and insert are made from material of the group consisting of copper and brass, and the insert is bonded to the inside wall of the tube by another and low-melting-point metal.

6. The heat exchanger described in claim 1 and in which the inside wall of the tube is coated with a solder and the Wire of the insert is also coated with a solder, and the insert is bonded to the Wall of the tube by these solders.

7. The heat exchanger described in claim 1 and in which the insert is welded to the inside wall of the tube.

8. The heat exchanger described in claim 7 and in which the tube and insert are made of stainless steel.

9. The heat exchanger described in claim 1 and in which the insert is bonded to the inside wall of the tube by metal fused to the tube wall and to loops of the insert adjacent to the tube wall.

10. The heat exchanger described in claim 1 and in which the insert has a center core and spokes extending from the center core into contact with the inside surface of the tube.

11. The heat exchanger described in claim 10 and in 6 which the insert has four spokes and has the general cross section of a cross.

12. The heat exchanger described in claim 10 and in which there are at least five spokes angularly spaced from one another around the entire circumference of the tube.

13. The heat exchanger described in claim 10 and in which the insert has a generally star-shaped cross section.

References Cited by the Examiner UNITED STATES PATENTS 666,785 1/01 Williams 158-53 1,273,436 7/ 18 Willson 165-119 X 1,289,910 12/18 Putnam 158-53 1,752,670 4/30 Kingman 165-119 1,809,654 6/31 Wagner 165-181 X 1,867,163 7/32 Loebell 165-10 X 2,032,134 2/36 Larkin 138-38 2,044,952 6/36 Neveu 165-180 X 2,254,587 9/41 Williams 165-180 X 2,289,163 7/42 Andersen 138-38 2,335,687 11/43 Modine 138-38 2,424,612 7/47 Gunter 138-38 2,587,252 2/52 Van Weenen et al 29-1573 2,616,668 11/52 Van Weenen et al. 165-10 2,722,733 11/55 Meyer et al. 29-1573 2,898,091 8/59 Verbeek 165-10 2,929,408 3/60 Weatherwax et al. 29-1573 X 2,960,114 11/60 Hinde 29-1573 X 3,053,246 9/62 Kosarin et al. 138-38 FOREIGN PATENTS 531,211 10/56 Canada.

602,889 6/ 48 Great Britain.

CHARLES SUKALO, Primary Examiner.

HERBERT L. MARTIN, FREDERICK L. MATTESON,

Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,195,627 July 20, 1965 Alfred Minor Goodloe It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 50, for "out" read but Signed and sealed this 21st day of December 1965.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner of Patents 

1. A HEAT EXCHANGER INCLUDING A METAL TUBE, (A) KNITTED WIRE MESH INSERT FORMED OF WIRE LOOPS AND LOCATED WITHIN THE TUBE, (B) THE INSERT BEING OF MUCH GREATER LENGTH THAN WIDTH AND HAVING ITS LENGTH EXTENDING AXIALLY IN THE TUBE, (C) THE LOOPS BEING CROWDED TOGETHER TRANSVERSELY OF THE LENGTH OF SAID INSERT OUT WITH THE CROWDED LOOPS OF THE WIRE MESH IN POSITION TO CONTACT WITH FLUID FLOWING ALONG THE INSIDE OF THE TUBE TO PRODUCE TURBULENCE OF THE FLUID ADJACENT TO THE WIRE MESH, (D) THE INSERT BEING SHAPED WITH PARTITION OR WALL PORTIONS OF DOUBLE WALL MESH AND HAVING A SYMMETRICAL PATTERN ABOUT A LONGITUDINAL AXIS OF THE TUBE, THE PARTITION PORTIONS DIVIDING THE INTERIOR OF THE TUBE INTO A PLURALITY OF AXIALLY-EXTENDING PASSAGES, (E) THE PARTITION PORTIONS HAVING FACES SPACED FROM THE INSIDE SURFACE OF THE TUBE ACROSS EXTENDING ANGULAR SIGNS OF THE CIRCUMFERENCE OF THE TUBE SO THAT 